BACKGROUND: Spontaneous tubal twin pregnancy is a rare condition with an incidence of 1 in every 125,000 pregnancies. We present the case of a unilateral tubal twin ectopic pregnancy treated with single-dose methotrexate.CASE: A 26-year-old nulliparous woman was admitted to our clinic with a complaint of vaginal bleeding and leftside pelvic pain. Her serum β-human chorionic gonadotropin (β-hCG) level was 18,780 mIU/mL and ultrasound revealed tubal twin pregnancy of 7 weeks' gestation. Because her vital signs were stable and no sign of tubal rupture was present, we performed single-dose (100 mg) methotrexate intramuscularly. In the follow-up, serum β-hCG levels were found to be 7,600 mIU/ml on day 7, 948 mIU/ml on day 20, 126 mIU/ml on day 26 and <10 mIU/ml on day 42.CONCLUSION: Methotrexate theraphy may be preferred in tubal twin ectopic pregnancies when the vital signs of the patient are stable and the fetal cardiac activities are negative.